Radiative Heat Transfer via Fins in a Steam Reformer

ABSTRACT

Embodiments are disclosed that relate to increasing radiative heat transfer in a steam reformer from an exterior shell which includes a diffusion burner to an interior reactor via angled fins coupled to the exterior shell. For example, one disclosed embodiment provides a steam reformer, comprising an exterior shell which includes a diffusion burner and angled fins, the angled fins extending away from an inner surface of the exterior shell and downward toward the diffusion burner. The steam reformer further comprises an interior reactor positioned at least partly within the exterior shell.

TECHNICAL FIELD

The present disclosure relates to the field of reforming, and moreparticularly, to a methane steam reformer for generating hydrogen foruse in a fuel cell.

BACKGROUND

In a steam reformer, under high temperatures (e.g., 400-800° C.) and inthe presence of a catalyst (e.g., nickel), steam may react with a feedgas (e.g., methane) to generate a reformate (e.g., hydrogen) which maybe used as fuel in a hydrogen fuel cell to generate electricity, forexample. Because the reforming reaction is endothermic, a heat source isneeded to maintain a temperature range at which the reaction can occur.In some examples, the steam reformer may include a burner outside of areactor which heats the reactor and is fueled by the reformate.

SUMMARY

Accordingly, various embodiments are disclosed herein related to usingan external shell for the steam reformer which includes a diffusionburner and angled fins in order to increase radiative heat transfer fromthe flame within the external shell (from the diffusion burner) to theinterior reactor. For example, one disclosed embodiment provides a steamreformer comprising an exterior shell which includes a diffusion burnerand angled fins, the angled fins extending away from an inner surface ofthe exterior shell and downward toward the diffusion burner. The steamreformer further comprises an interior reactor positioned at leastpartly within the exterior shell.

In such an example, the angled fins behave as a baffle to direct flow ofthe combustion gases (e.g., burning hydrogen) and as thermal radiationemitters. As such, an amount of heat transferred to the interior reactormay be at least partially controlled by a position, angle, and length ofeach angled fin coupled to an inner surface of the exterior shell. Bycontrolling the amount of heat transferred to the interior reactor, areforming reaction which occurs within the interior reactor may bedriven toward the formation of more products, for example.

It will be understood that the summary above is provided to introduce insimplified form a selection of concepts that are further described inthe detailed description, which follows. It is not meant to identify keyor essential features of the claimed subject matter, the scope of whichis defined by the claims that follow the detailed description. Further,the claimed subject matter is not limited to implementations that solveany disadvantages noted above or in any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure will be better understoodfrom reading the following detailed description of non-limitingembodiments, with reference to the attached drawings, wherein:

FIG. 1 shows a block diagram of a steam reforming system coupled to afuel cell stack in accordance with an embodiment of the presentdisclosure.

FIG. 2 schematically shows a cross-sectional view taken along an axialdirection of an example embodiment of an exterior shell that may be usedin a steam reformer.

FIG. 3 schematically shows another view of the exterior shell of FIG. 2in accordance with an embodiment of the present disclosure.

FIG. 4 shows a block diagram illustrating flows of gas and energy in asteam reformer in accordance with an embodiment of the presentdisclosure.

FIG. 5 shows a flow chart illustrating a method for a steam reformercoupled to a fuel cell stack in accordance with an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

The following description relates to various embodiments of a steamreformer which includes an external shell with angled fins configured toallow a greater intensity of radiative heat to reach an interior reactorthan a similar external shell without angled fins. As described in moredetail below, such angled fins may be coupled to the exterior shell, forexample, at locations and angles such that heat from combustion of gasesrising from a diffusion burner positioned in a bottom portion of theexternal shell may be transferred to the fin and may be radiated to adesired location of the interior reactor. This may facilitate increasedheating of the interior reactor in order to drive a reforming reactionin the interior reactor toward the formation of more products (e.g.,hydrogen) compared to the same interior reactor surrounded by anexternal shell without the angled fins.

In some examples, the burner may be positioned below a reactor such thatheat from combustion of a fuel, such as hydrogen generated by thereformer, rises up around the reactor or through a center portion of thereactor. Due to the buoyancy of hydrogen in air, the hydrogen flamesfrom the burner may ascend rapidly resulting in a relatively low amountof heat transferred to the reactor, especially in a lower region of thereactor. Further, a length of the reactor may be limited by a space inwhich the reactor is used, for example, resulting in a relatively shortlength of time for the burning hydrogen to heat the reactor. As such,the reactor may not receive a desired amount of heat to facilitate thereforming reaction, especially in a lower region of the reactor wheremore heat is needed due to cooling of the reformate stream from theendothermic reforming reaction (e.g., when the reformate travels from atop end of the reactor to a bottom end of the reactor).

FIG. 1 shows an example embodiment of a system 100 including a reformer102 coupled to a fuel cell stack 104. Reformer 102 may generate aproduct stream that contains hydrogen gas, for example. Hydrogen that isgenerated in steam reformer 102 may be utilized, for example, by fuelcell stack 104 to generate electrical power. The hydrogen may be furtherutilized to fuel a diffusion burner positioned within an exterior shell108 which surrounds an interior reactor 106 of the steam reformer 102.Reformer 102 may be a steam reformer, for example, which converts amixture of steam and a feed gas such as methane to hydrogen and carbonmonoxide and/or carbon dioxide. In other embodiments, reformer 102 maybe an autothermal reformer.

In the example embodiment of FIG. 1, the interior reactor 106 issupplied with a mixture of feed gas (e.g., methane or other suitablereactant) and water at 110. The mixture of feed gas and water may beproduced in any suitable manner. For the purpose of describing operationof the reactor, the examples described herein will assume the feed gasis methane. It should be understood, however, any suitable feed gas maybe used. In some embodiments, the methane/water mixture may be convertedto a gaseous mixture by a vaporizer (not shown) before entering interiorreactor 106. In other embodiments, methane and water may be heated sothat they are in gaseous form before they are mixed.

In some embodiments, the interior reactor 106 may have a cylindricalshape and a reaction chamber 107 within the interior reactor may have ahollow shape, such as the depicted ring shape, or other suitable shapethat surrounds and conforms to the shape of the interior reactor. Thereaction chamber 107 may be filled with a packing material. For example,the packing material may be a metal-based catalyst such as nickel whichfacilitates the reaction of feed gas and steam within reaction chamber107. For example, in the presence of packing material and at hightemperature (e.g., 750° C.), methane reacts with steam to form hydrogenand carbon monoxide via the following reversible reaction:

CH₄+H₂0

CO+3H₂.  (1)

As will be described in more detail below with reference to FIGS. 2 and3, exterior shell 108 includes a burner, such as a diffusion burner, forheating the reactor to a temperature for the reaction to occur. As shownin FIG. 1, exterior shell 108 surrounds a portion of the interiorreactor extending from a bottom end of the interior reactor 106partially toward a top end of the interior reactor 106 (e.g., the endwhere feed gas enters the interior reactor). Exterior shell may cover60% of the outer wall, for example, when the interior reactor restsinside the exterior shell. Exhaust from combustion that occurs within acavity formed by the external shell may be used to heat the feedgas/water mixture before it enters reaction chamber 107. In someembodiments, the reformer 102 may further include a recuperator 112which surrounds a portion of the outer wall of the interior reactor 106extending from a top portion of the external shell 108 toward the topend of the interior reactor. The recuperator may be used to heat ormaintain a high temperature in the upper part of reaction chamber 107using exhaust gas from the diffusion burner or exhaust gas from the fuelcell stack 104 to which the interior reactor 106 supplies fuel, forexample. It will be understood that heat may be provided to interiorreactor 106 in any other suitable manner, and that the above-describedembodiment is not intended to be limiting in any manner.

Reformate (e.g., hydrogen gas) generated in reaction chamber 107 of theinterior reactor 106 exits the reaction chamber at a bottom portion ofthe interior reactor and travels through an inner chamber 109 beforeexiting the interior reactor 106 at its top end. As shown in the exampleof FIG. 1, hydrogen is routed from the reformer to the fuel cell stack104 via a first pipe 114. The first pipe 114 may have a diameter inaccordance with, for example, a desired amount and/or pressure ofhydrogen to be supplied to the fuel cell stack 104 based on a flow rateand pressure of hydrogen generated in the interior reactor 106. Thefirst pipe 114 may be made of any suitable material for transportinghydrogen, for example, stainless steel. It will be understood that theterm “pipe” signifies any suitable structure for carrying gases such asa tube, a hose, a manifold, etc.

Fuel cell stack 104 may be configured to generate power from a reactionbetween the supplied fuel (e.g., hydrogen) and oxidant for driving anexternal load. In some embodiments, the fuel cell stack 104 may includea plurality of fuel cells that may be electrically connected to generatea higher voltage. For example, the fuel cell stack 104 may include aplurality of fuel cells electrically connected in series.

System 100 further includes a valve 116 for regulating a supply of afuel to the fuel cell stack 104. Valve 116 may be controlled via acontroller (not shown) to route a first portion of the hydrogengenerated in the interior reactor 106 to the fuel cell stack 104. Valve116 may be further controlled to route a second portion of hydrogen tothe diffusion burner (not shown) positioned within the bottom portion ofthe external shell 108 via a second pipe 118. For example, valve 116 maybe a three-way valve. Second pipe 118 may have similar characteristics(e.g., diameter, material, etc.) as the first pipe 114, for example. Itwill be understood that the depicted fuel delivery system (e.g., firstand second pipes 114 and 118 and valve 116) is shown for the purpose ofexample, and that any other suitable component or components may beutilized to supply hydrogen to the diffusion burner and the fuel cellstack 104.

Continuing to FIGS. 2 and 3, detailed examples of an embodiment of anexternal shell 200, such as external shell 108 of FIG. 1, are shown. Asdepicted in the examples of FIGS. 2 and 3, external shell 200 has acylindrical shape with a tapered portion near a top end of the externalshell resulting in a diameter at the top end less than that of adiameter at a bottom end of the external shell, similar to the shape ofa milk can, for example. External shell 200 may be formed of anysuitable material that is capable of withstanding the high temperatureof burning hydrogen and insulating the interior reactor. For example,the exterior shell may be made of high nickel content stainless steelalloy.

As shown in the examples of FIGS. 2 and 3, which are drawn to scale, adiffusion burner 202 is positioned in a bottom portion of the externalshell. Hydrogen from the interior reactor is fed to diffusion burner 202via inlet 204. As shown in the example FIG. 3, external shell 200 mayinclude additional inlets 206 and 208 for supplying diffusion burner 202with ambient air and/or another combustible fuel, such as a hydrocarbonor alcohol fuel, for example. In some embodiments, hydrogen and air aremixed within the diffusion burner to form an oxygenated combustible fuelstream before being routed to the cavity 210 which is formed between theexternal shell 200 and an interior reactor (not shown in FIGS. 2 and 3)when the external shell surrounds the interior reactor, for example. Inother embodiments, the fuel stream may be mixed before entering theburner.

Diffusion burner 202 routes the combustible fuel (e.g., hydrogen andair) into cavity 210 where it is ignited via a spark from igniter 212.Flames from the burning hydrogen rise upward toward the top of theexternal shell 200.

Further, external shell 200 includes two angled fins, first angled fin214 (the upper fin) and second angled fin 216 (the lower fin) which areshaped to conform to the exterior shell. For example, the depicted finsare ring-shaped to conform to the shape of the depicted exterior shell.In other embodiments, the external shell may include one angled fin ormore than two angled fins. Each angled fin may extend the same radialdistance from the inner surface of the exterior shell, as shown in FIGS.2 and 3. For example, angled fins 214 and 216 extend to a radialdistance 222 that is 90% of a distance 224 between the inner surface ofthe exterior shell and an outer surface of the interior reactor (whenthe exterior shell surrounds the interior reactor). In other examples,the angled fins may extend to different radial distances across thecavity. Furthermore, in the example of FIGS. 2 and 3, angle 218 betweenangled fin 214 and the inner surface of the exterior shell is less thanangle 220 between angled fin 216 and the inner surface of the exteriorshell. As such, a length 226 of the upper fin is greater than a length228 of the lower fin. It should be understood that FIGS. 2 and 3 aremerely examples, and an external shell may include any suitable numberof angled fins

Angled fins 214 and 216 may be made of solid or perforated metal orceramic material. In such an embodiment, the angled fins behave asbaffles to the flow of the combustion gases, as combustion gases heatextraction devices, and as directed thermal radiation emitters. Forexample, the angled fins receive energy from the combustion gases andfrom any other radiating surface in the burner cavity. The fins may besolid or may contain some perforations. The solid part of the finbehaves as a baffle to impede the flow of the combustion gases andintroduce recirculation to the burner chamber thereby increasingconvective heat transfer. When perforations are used, the perforations215 in the angled fins allow for combustion gases to pass through thefins and, as the combustion gases pass through the perforations, energyis transferred convectively to the fins. This energy may then betransferred via radiation to the interior reactor. Size, shape, andlocation of the perforations 215 in each angled fin may be determinedsuch that convective heat transfer to the fins from the combustion gasesis increased while the cumulative radiation heat transfer through theperforations is decreased, for example. As such, each angled fin coupledto the external shell may have perforations with differentcharacteristics (e.g., perforations are larger on the bottom fin thanthe top fin). As an example the perforations may be round holes ⅛ inchin diameter.

Furthermore, position, length and angle of the angled fins may bedetermined such that a desired amount of heat is radiated to a desiredlocation of the interior reactor in order to drive a reforming reactionin the interior reactor toward the formation of more products and basedon a length of the reactor, for example. As an example, the angled finsmay be located near a middle region of the exterior shell whichcorresponds to a lower region of the interior reactor where more heatmay be needed due to cooling of the reformate stream from theendothermic reforming reaction. As such, the interior reacted may beheated to a desired temperature at a desired location without extendingthe length of the reformer.

Exterior shell 200 further includes temperature sensors 230 and 232positioned below angled fins 214 and 216, respectively. As shown mostclearly in FIG. 2, temperature sensors 230 and 232 extend from outsideof the exterior shell 200 and into the cavity 210 toward the interiorreactor. In embodiments which include more or less angled fins, more orless temperature sensors may be included, for example, such that eachangled fin has a corresponding temperature sensor. The temperaturesensors may be used to determine temperature in the vicinity of eachtemperature sensor so that more or less air and/or hydrogen may bedelivered to the diffusion burner in order to increase or decreasetemperature based on a desired temperature in the vicinity of eachangled fin, for example.

FIG. 4 shows gas and energy flow within an embodiment of a steamreformer 400, such as steam reformer 102 described above with referenceto FIG. 1. For example, energy is provided by combustion flamescontained within the region formed between the external shell and theinterior reactor as well as by the reformate that flows through theinterior reactor.

A path of the burner gas (e.g., hydrogen and air) through the externalshell 401 is indicated by the arrows containing horizontal lines in FIG.4. As illustrated, the burner gas flows through burner 402 and upwardtoward angled fin 404. Angled fin 404 extracts heat from the combustiongasses and focuses radiation directed at an angle toward an upperreactor region 406 of the interior reactor before it flows out of theexternal shell and into the recuperator.

A path of the reformate gas through the interior reactor is indicated bythe arrows containing diagonal lines in FIG. 4. As illustrated, thereformate gas (e.g., hydrogen) first flows through a reaction chamber ofthe interior reactor 405, the reaction chamber including upper 406,center 408, and lower 410 regions. The reformate then exits the reactionchamber and enters the inner chamber of the interior reactor 413. Thereformate gas is then routed from a bottom portion of the interiorreactor to a top portion of the interior reactor where it is routed to afuel cell and/or back to the diffusion burner, as described above.

Further, paths of energy flows used to bring about a reforming reactionare indicated by arrows containing dots in FIG. 4. As described above,the reforming reaction which converts methane and steam to hydrogen inthe presence of a catalyst occurs at high temperatures (e.g., 400-800°C.). Thus, the burner 402 is provided outside of the interior reactor inorder to heat the interior reactor. As shown in FIG. 4, the angled fin404 may be positioned such that the interior reactor receives a greateramount of heat than it would in a similar steam reformer that does notinclude angled fins.

The steam reformer 400 of FIG. 4 further includes a radiative shunt 412near the central reactor region 408 which is configured to allow agreater intensity of radiative heat to reach farther into a reactor thana similar reactor without a shunt, as indicated by the arrow.

The flow chart in FIG. 5 illustrates an embodiment of a method 500 for asteam reformer coupled to a fuel cell stack, such as steam reformer 102and fuel cell stack 104 shown in FIG. 1.

At 510 of method 500, feed gas and steam are delivered to the interiorreactor. As described above, the feed gas may be methane or anothersuitable reactant. Hydrogen is then generated at 512 of method 500 asthe feed gas travels through the interior reactor and is converted tohydrogen in the presence of a catalyst and high temperatures.

Once hydrogen is generated, a first portion of the hydrogen is deliveredto the fuel cell stack to generate electricity at 514. For example, afirst pipe routes the hydrogen to the fuel cell stack and the amount ofhydrogen routed to the fuel cell stack is controlled via adjustment of avalve. A second portion of hydrogen is routed to an inlet of thediffusion burner at 516 of method 500. For example, the valve may becontrolled to route the second portion of hydrogen to the diffusionburner via a second valve.

Hydrogen that is routed to the diffusion burner is then burned in thecavity formed by the exterior shell at 518 of method 500. Heat from thehydrogen flames is directed toward the angled fins to heat the reactorat 520 of method 500.

Thus, an external shell which includes one or more angled fins may beused to increase an amount of heat transferred to an interior reactorwhich it surrounds without extending the length of the reformer comparedto an external shell that does not have angled fins. For example, theamount of heat transferred to the interior reactor may be at leastpartially controlled by a position, angle, and length of each angled fincoupled to an inner surface of the exterior shell. By controlling anamount of heat transferred to the interior reactor via the angled fins,a reforming reaction which occurs within the interior reactor may bedriven toward the formation of more products.

It will be understood that some of the process steps described and/orillustrated herein may in some embodiments be omitted without departingfrom the scope of this disclosure. Likewise, the indicated sequence ofthe process steps may not always be required to achieve the intendedresults, but is provided for ease of illustration and description. Oneor more of the illustrated actions, functions, or operations may beperformed repeatedly, depending on the particular strategy being used.

Finally, it will be understood that the articles, systems and methodsdescribed herein are exemplary in nature, and that these specificembodiments or examples are not to be considered in a limiting sense,because numerous variations are contemplated. Accordingly, the presentdisclosure includes all novel and non-obvious combinations andsub-combinations of the various systems and methods disclosed herein, aswell as any and all equivalents thereof.

1. A steam reformer, comprising: an exterior shell which includes adiffusion burner and angled fins, the angled fins extending away from aninner surface of the exterior shell and downward toward the diffusionburner, the exterior shell forming a cavity in which combustion occurs;and an interior reactor positioned at least partly within the exteriorshell, wherein at least a portion of the cavity extends between theangled fins and the interior reactor.
 2. The steam reformer of claim 1,wherein the exterior shell includes two angled fins which are ringshaped, and wherein an angle between an upper of the two angled fins andthe exterior shell is less than an angle between a lower of the twoangled fins and the exterior shell.
 3. The steam reformer of claim 1,wherein the angled fins extend to a radial distance that is 90% of adistance between the inner surface of the exterior shell and an outersurface of the interior reactor.
 4. (canceled)
 5. The steam reformer ofclaim 1, wherein the diffusion burner is in a bottom portion of theexterior shell.
 6. The steam reformer of claim 1, further comprising afirst pipe extending from a top end of the interior reactor throughwhich a first portion of hydrogen generated in the interior reactor isrouted to a fuel cell coupled to the steam reformer.
 7. The steamreformer of claim 6, further comprising a second pipe coupled to thefirst pipe via a valve, the second pipe routing a second portion ofhydrogen generated in the interior reactor to an inlet of the diffusionburner for fuel.
 8. The steam reformer of claim 1, further comprisingtemperature sensors positioned below each angled fin, the temperaturesensors extending from outside the exterior shell toward the interiorreactor. 9-20. (canceled)
 21. The steam reformer of claim 1, wherein aportion of the interior reactor not surrounded by the external shell issurrounded by a recuperator.
 22. The steam reformer of claim 1, whereinthe angled fins are made of solid or perforated metal or ceramicmaterial, the perforations such that combustion gases pass through.